Dynamic Analysis Of The Content Of Lactic Acid And Bacterial Community Structure During The Fermentation Of Fen-Flavor Baijiu

During the fermentation of Fen-flavor Baijiu,excessive lactic acid and its derived esters in the fermented grains can adversely affect Baijiu,while the microbial community structure in the fermented grains is closely related to the content of lactic acid.Therefore,the analysis of the bacterial community structure and the changes in the content of lactic acid and ethyl lactate during the fermentation of Fen-flavor Baijiu are of great significance to the improvement of the flavor and quality of Fen-flavor Baijiu.Current research on Fen-flavor Baijiu focuses on the flavor substances in the body of the liquor and the changes of microbial community in the fermented grains during a specific period,but there is a lack of research on lactic acid and its derived esters in fermented grains and comparative investigation of the three different brewing stages of the Li Pei Qi,cold season and hot season.This study used metabolomics and macrogenomics techniques to correlate lactic acid,ethyl lactate,and microbial community structure in fermented grains during the Li Pei Qi,cold season and hot season,and identified key microorganisms affecting lactic acid excess in the hot season by comparing the results of the cold and hot seasons.At the same time,the dominant acid-producing strains in the fermented grains were isolated and screened,and the acid-producing ability and environmental tolerance of each strain were studied.This study provides theoretical basis for controlling the lactic acid content in Baijiu and further improving the quality of Fen-flavor Baijiu.The main research contents and results of the paper are as follows:（1）The analysis of the changes in the contents of lactic acid and its derived esters during the fermentation of Fen-flavor Baijiu during the Li Pei Qi and the structural changes of the bacterial flora in the Li Pei Qi revealed that Firmicutes was always dominant during the fermentation of Fen-flavor Baijiu,and Lactobacillus under the Firmicutes was always absolutely dominant during the whole fermentation process.Therefore,the content of lactic acid,a metabolite of Lactobacillus,was always high during the fermentation process.The lactic acid content of fermented grains during the fermentation is closely related to the bacterial flora structure.The relative abundance of L.plantarum was positively correlated with the change of lactic acid content in Dacha,and the change in relative abundance of L.acetotolerans in Ercha was positively correlated with the change in lactic acid content in Ercha.Therefore,L.plantarum and L.acetotolerans were the key strains affecting the lactic acid production in the fermentation of Fen-flavor Baijiu during Li Pei Qi.（2）A comparative study of the changes in lactic acid and its derived ester content and bacterial flora structure in the fermentation of Fen-flavor Baijiu in cold and hot seasons revealed that the temperature in different seasons had a greater influence on the content of lactic acid and ethyl lactate in fermented grains,and the changes in lactic acid content during the fermentation of Fen-flavor Baijiu mainly occurred in the pre-fermentation period.The Hiseq platform was used to analyze 10 genera of 4 phyla,22 orders,5 families and 8 families from fermented grains in cold season,and 15 genera of 5 phyla,22 orders,7 families and 15 families from fermented grains in hot season.The results showed that the bacterial species in fermented grains became more diverse as the fermentation progressed in both cold and hot seasons.In the later stages of fermentation,the number of bacteria during the fermentation in hot season gradually increased,while the number of bacteria during the fermentation in cold season decreased significantly.Lactobacillus was the dominant genus in both cold and hot seasons.The correlation analysis of lactic acid,ethyl lactate content and bacterial flora structure showed that L.acetotolerans was the key microorganism causing the difference in lactic acid content during the fermentation of cold and hot seasons,L.plantarum was the main lactic acid producing bacteria.（3）Five strains of acid-producing microorganisms were screened from the fermented grains at the late 15 and 21 pairs in Li Pei Qi,among which L.coryniformis LC has stronger acid production ability and strongest alcohol tolerance,although it can also tolerate the acid environment of p H2.5,but the OD₆₀₀ value is lower in the acid environment of p H4.5;Pediococcus acidilactici PA has stronger acid production ability and can tolerate the acid environment of p H2.5.Therefore,strain LC and strain PA have strong acid production,acid tolerance and alcohol tolerance.The screened strains have potential value for improving the flavor taste of Fen-flavor Baijiu.Twelve strains of acid-producing microorganisms were screened from fermented grains at the end of fermentation in cold and hot season.At the plateau stage of fermentation,L.plantarum LP had the lactic acid concentration of 6.82 g·L^-1 at the end of fermentation;at the stable stage of fermentation,the p H of Lacticaseibacillus rhamnosus LR was as low as 3.63,so strain LP has a strong lactic acid production capacity,and strain LR has a strong acid production capacity.The OD₆₀₀ value of strain LH remained stable at p H 4.0,and the OD₆₀₀ value was 0.77 at p H 3.0;with the increase of ethanol concentration,the OD₆₀₀ value of strain LH slightly decreased,so strain LH has the characteristics of acid and alcohol tolerance at the same time.This provides a reference for the effective reduction of lactic acid content during the fermentation of Fen-flavor Baijiu in summer.